Flex pipe ahead of CAT, another Choke Point.

warp2diesel · **Posted:** Wed Dec 04, 2013 4:28 pm

My flex pipe ruptured and needed to be replaced:

What I bought to replace it a 2 1/2" ID Flex pipe:

To get it out so I could weld in the new flex pipe, I had to drop the transmission cross member:

And move stuff out of the way on top:

When I cut the old flex pipe, I found some more Bean Counter Engineering, they used one with a choked down size of 2.099" instead of a true 2.5" to save a few cents:

Cleaned up the rust so could MIG weld the new flex pipe in. Don't forget to position and tack in place first:

Now I have more pep, the boost gauge climbs faster, and a little more exhaust rumble noise when I get on it.
No more smells in the cab.

CRD05il · **Posted:** Wed Dec 04, 2013 5:23 pm

What kind of smell did you have?

bugnout · **Posted:** Wed Dec 04, 2013 5:28 pm

Nice writeup.

Was the exhaust noise more noticeable with the rupture or was it caught with a visual inspection?

warp2diesel · **Posted:** Wed Dec 04, 2013 6:30 pm

CRD05il wrote:

What kind of smell did you have?

Exhaust smell that did not pass through the CAT/Soot Trap that changes the smell a little.
My wife is on Blood Pressure Meds that enhance her sense of smell and taste of some foods.
Even the EPA knows about the Blood Pressure Drug Side Effects and has it well documented to hand to their dweebs.

warp2diesel · **Posted:** Wed Dec 04, 2013 6:34 pm

bugnout wrote:

Nice writeup.

Was the exhaust noise more noticeable with the rupture or was it caught with a visual inspection?

My 5/16" torque converter bolts stripped and sheared off when I was too far from home so I had a local Tech fix it by tapping them out to 10mm (Suncoast recommended fix). The tech caught the leak when it was small and even I smelled it when it got bad, of course, my wife smelled it long before I did. Toward the end, the noise was loud enough for even me to hear.

thermorex · **Posted:** Wed Dec 04, 2013 6:39 pm

Warp, you should move this thread in tech forum. Nice write-up!

flash7210 · **Posted:** Wed Dec 04, 2013 10:11 pm

What is the purpose of the flex pipe?
Why not it weld in a solid pipe?

airwerks · **Posted:** Thu Dec 05, 2013 4:23 pm

Exhaust systems have to be allowed to flex whether through a flex pipe like we have or a ball/donut style on other cars. Otherwise cracking and short gasket life is the result.

flash7210 · **Posted:** Fri Dec 06, 2013 8:30 am

The reason I ask is for decades cars/trucks got along just fine without a fancy flex joint.
The CRD has a "ball" type joint after the cat. Wouldn't that alone be enough?

airwerks · **Posted:** Fri Dec 06, 2013 4:25 pm

Most of my cars are older.... and all of them have a donut / ball joint in close proximity to the engine to account for motor mounts flexing and expansion of exhaust pipes with heat. This just takes the place of that. IMO the cat is far to away from the rotational center of where the motor mounts allow the engine to move to accomplish the same feat.

jagster936 · **Joined:** Sun Aug 04, 2019 3:06 pm **Posts:** 210

Thread resurrection! I just found a leak in my flex joint also. I have been chasing this hissing noise, actually for years lol. Always thought it was an intake exhaust leak. My mechanic friend held a rag at the bag of exhaust and immediately we identified the hiss at the flex joint.

What is the best approach to repair? What you did? Do people delete the flex entirely or just buy another one somewhere? The OP removed the section of exhaust and welded on the new flex?

Jeep has 118k miles hopefully I don't need a new cat or anything, or just straight pipe it but I don't want any stupid loud noises.

Thanks!

WWDiesel · **Posted:** Mon Jun 06, 2022 10:37 pm

Get rid of the CAT and the choke point in front of it if you don't have to withstand any inspections. There are NO sensors on this vehicle monitoring the CAT function so if you remove it, it will not set any DTC's. The engine will rung better without it and turbo spool up response time will improve along with lowering EGT's coming out of the head due to lower back pressure.

As to the flex pipe, any good muffler shop should be able to supply with a new one and replace it with a universal 2.5 X 8 inch flex pipe.
or order it online. They are relatively inexpensive.

Amazon even lists them:>
2.5"(I.D.) X 8"(L) X 12"(OL) Exhaust Flex Pipe Universal Fit Flex Tube Stainless Steel
https://www.amazon.com/I-D-Exhaust-Univ ... B008KQ9Y80

jagster936 · **Joined:** Sun Aug 04, 2019 3:06 pm **Posts:** 210

I saw that! Nice, will do.

From my reading people say removing the cat may not do much, the restriction in front of or behind may matter. But more than anything the muffler is the restriction point. I don't want a noisy or droning machine either.

WWDiesel · **Posted:** Tue Jun 07, 2022 1:52 am

jagster936 wrote:

I saw that! Nice, will do.
From my reading people say removing the cat may not do much, the restriction in front of or behind may matter. But more than anything the muffler is the restriction point. I don't want a noisy or droning machine either.

I have a 2.5" Flowmaster muffler and No CAT with OEM tailpipe out to the rear. It makes a nice low mellow sound; cannot even hear it with windows rolled up.

jagster936 · **Joined:** Sun Aug 04, 2019 3:06 pm **Posts:** 210

Nice I’d love to hear that. Any noticeable mpg or turbo differences?

I measured from appeared weld point to weld was about 10.5 inch. Does it go by length of braid or From the welds?

WWDiesel · **Posted:** Tue Jun 07, 2022 12:44 pm

jagster936 wrote:

Nice I’d love to hear that. Any noticeable mpg or turbo differences?
I measured from appeared weld point to weld was about 10.5 inch. Does it go by length of braid or From the welds?

I don't really worry much about MPG, I drive it for the torque.
NO CAT improves turbo response time and lowers EGT coming out of head.

Measurement of flex pipe I would think is end to end! But even if it is a little longer that is not a problem, just use a shorter piece of 2.5" pipe to connect from it to the muffler in place of CAT. :wink:

taroo · **Joined:** Sun Apr 27, 2008 2:14 pm **Posts:** 278

WWDiesel wrote:

jagster936 wrote:

I saw that! Nice, will do.
From my reading people say removing the cat may not do much, the restriction in front of or behind may matter. But more than anything the muffler is the restriction point. I don't want a noisy or droning machine either.

I have a 2.5" Flowmaster muffler and No CAT with OEM tailpipe out to the rear. It makes a nice low mellow sound; cannot even hear it with windows rolled up.

And where did you get all the other pipes? I think I recall you posted a link at one point. I would like to cut ahead of the cat, install your recommended FLOWMASTER 40 SERIES DELTA FLOW CHAMBERED MUFFLER and just go out the back with a tailpipe. So I will need the pipes in between.

WWDiesel · **Posted:** Wed Nov 22, 2023 1:10 pm

Flex pipe remains. Cut exhaust pipe just in front of the CAT and right behind OEM muffler. Using a straight piece of 2.5" exhaust tubing flared on one end to slip over the OEM head pipe. The Flowmaster muffler will slip over the OEM tailpipe (weld or clamp w/heavy duty clamp). Cut new 2.5" tubing to correct length to fit inside Flowmaster Muffler. (Flowmaster muffler inlet and outlet is sized/flared to allow 2.5" pipe to fit inside both ends)
Flowmaster 942542 Series 40 Delta Flow, 2.50 Center In / 2.50 Offset Out

taroo · **Joined:** Sun Apr 27, 2008 2:14 pm **Posts:** 278

WWDiesel wrote:

Flex pipe remains. Cut exhaust pipe just in front of the CAT and right behind OEM muffler. Using a straight piece of 2.5" exhaust tubing flared on one end to slip over the OEM head pipe. The Flowmaster muffler will slip over the OEM tailpipe (weld or clamp w/heavy duty clamp). Cut new 2.5" tubing to correct length to fit inside Flowmaster Muffler. (Flowmaster muffler inlet and outlet is sized/flared to allow 2.5" pipe to fit inside both ends)
Flowmaster 942542 Series 40 Delta Flow, 2.50 Center In / 2.50 Offset Out

Perfect...thanks much. My next project for the Libby!

Flex pipe ahead of CAT, another Choke Point.

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